The invention concerns a closing unit of an injection molding machine. An injection molding process generally begins with closure of the closing unit, by the moveable mold mounting plate being moved towards the fixed mold mounting plate by a fast-action stroke device. The moveable mold mounting plate is then locked with the pressure-applying piston member of a pressure mechanism, and the pressure mechanism builds up the closing pressure necessary for the injection process.
Frequently, one or more columns are used for guiding the moveable mold mounting plate. In the case of an injection molding machine having one column, the pressure mechanism is often a hydraulic cylinder whose piston exerts a pressure on the moveable mold mounting plate via the column. An injection molding machine having four columns, then also referred to as bars, is also a familiar structure. Here, the pressure mechanism is often in the form of a pressure cushion between the mold mounting plates or at the ends of the bars. Those pressure cushions are also often hydraulic as high pressures have to be built up in a relatively short time.
The subject-matter of the invention is closing units of injection molding machines. In these machines, after the working operation of the fast-action stroke, the columns are locked and the pressure mechanism is supported by way of the columns. In the foregoing examples, on the one hand the columns are locked to the piston member of the pressure mechanism, and on the other hand the bars are locked to the moveable mold mounting plate.
Locking actions of that kind are often implemented by two-part nuts which embrace the columns of the closing unit. That applies both in regard to closing units having one column and also closing units having four columns. To be able to easily open and close the two-part nut, it is advantageous for the halves of the nuts to be mechanically coupled in motionally opposite relationship to each other. Since, as in the above-described examples, the devices necessary for the hydraulic arrangement are often already present there, it is standard procedure in the state of the art to actuate both the fast-action stroke and also the two-part nuts hydraulically.
Disadvantages with hydraulic opening and closing of the nuts are a relatively long reaction time on the part of the hydraulic system and a lack of precise positional detection of the two-part nuts. This means that time is lost in each injection molding process, The hydraulic activation can lead to disturbances in operation or even to damage to the closing unit if the nut is not properly closed and consequently locking of the column is incomplete.
The aim of the invention is to provide a closing unit having a locking mechanism which does not suffer from the above-described disadvantages.